In general, skin cancer is more likely to be curable when the cancer is identified and treated early. Recognition of abnormal growth and changes to moles is one way to identify, at an early stage, moles with an increased risk of becoming cancerous.
Specifically, the American Academy of Dermatology (the AAD) states some moles may develop into a form of skin cancer known as malignant melanoma (www.aad.org/public/Publications/pamphlets/Moles.htm). On that web page, the AAD provides additional guidance, as follows:                Recognizing the early warning signs of malignant melanoma is important. Remember the ABCD's of melanoma when examining your moles.                    A stands for ASYMMETRY, when one half of the mole doesn't match the other half.            B stands for BORDER, when the border or edges of the mole are ragged, blurred or irregular.            C stands for COLOR, when the color of the mole is not the same throughout or if it has shades of tan, brown, black, red, white or blue.            D stands for DIAMETER, when the diameter of a mole is larger than 6 mm, about the size of a pencil eraser.                        If a mole displays any of these signs, it should be checked promptly by a dermatologist.        
Another factor that may point to an increased risk of cancer is a significant change in any of the above attributes over time. Heretofore, tracking the changes to moles over time has been a laborious process.
For instance, a specially trained photographer may take a predetermined number (e.g., 36) of digital photographs of a subject, carefully capturing each image from a predetermined distance, a predetermined perspective or angle, and with a predetermined camera rotation, relative to the subject. Collectively, the images may record a full-body image of the subject. The original set of images may be saved. At a later time, the specially trained photographer may take another full set of images using the same, careful procedure. Computer software may be used to store the images and to retrieve the images, to help a medical professional to manually compare before and after images to detect changes over time.